Due to higher requirements with regard to power, torque, gasoline consumption, and emissions, modern four-cycle combustion piston engines are in almost all cases provided with actuator devices for the phase shifting of the inlet and/or the exhaust camshaft through which the opening times and closing times of the inlet and/or exhaust valves can mainly be modified with regard to rotational speed and load. Through adequate phase adjustment of the inlet and exhaust camshafts, stable idling, increased torque at lower rotational speed of the motor, increased maximum performance and reduced pollutant emission at partial load operation of the respective combustion piston engine can be achieved.
Known actuator devices for the phase adjustment of a camshaft are designed as hydraulic rotary adjusters or as electromechanical rotary adjusters which are positioned immediately between a hub, provided with a chain or toothed belt loop, and the axle of the camshaft wheel which is connected in a rotationally fixed manner with the camshaft. However, disadvantages of such direct rotation adjuster devices are the required actuator forces and the large control effort for the setting of a certain phase angle.
For the improvement of the control characteristics, adjuster devices are therefore proposed for the phase adjustment of a camshaft, in which in the valve train, between the crankshaft and the camshaft, a phase shifter gearbox is provided which is in an operative connection with an adjustment driver. The phase shifter gearbox has generally two input elements and an output element, whereby the first input element, for instance via a chain or toothed belt, is in an operating connection with the crankshaft, the second input element is connected to a controllable adjustment drive, and the output element is connected in a rotationally fixed manner with the cam shaft.
A preferred use of a phase shifter gearbox is a simple planetary transmission or a coupled planetary transmission which comprises components of two planetary gear sets. The actuator drive can be designed as an auxiliary power controlled rotary drive, such as for instance as an electric motor or as a hydraulic rotary adjuster, or as a controllable brake device.
In view of its construction and its control, an especially simple and cost-effective brake device is designed as a friction brake which comprises an enclosure-mounted electromagnet with a magnet body and a magnet coil, as well as a rotationally fixed and axially shiftable brake rotor which is linked with the second input element and which can be pressed against an enclosure-mounted friction surface through the magnetic field of the electromagnet. Since the second input element would be rotating in the running condition faster than the first input element, adjustment of a certain, averaged brake torque is effective at the brake rotor and thus at the second input element, and a certain phase position of the assigned countershaft is maintained. Beginning at this phase position of the camshaft, an adjustment towards early is achieved through a brief increase of the brake torque, and towards late through a brief decrease of the brake torque.
An actuator device for phase adjustment of a camshaft with a phase shifter gearbox and with its operative connection of a brake device is known through DE 10 2006 011 806 A1. The phase shifter gearbox of this actuator device is designed as a coupled planetary transmission with two sun gears with different diameters and teeth count, as well as a planetary carrier which carries several rotatably mounted, two-step planetary gears, wherein the first input element is formed through the planetary carrier, the second input element through the smaller sun gear, and the output element through the larger sun gear.
The brake device is designed as an electromagnetic controllable friction brake which comprises a enclosure-fixed electrode magnet with a magnet body and a magnet coil, as well as a rotationally fixed and axially shiftably, connected with the smaller sun gear, and the brake rotor which can be pressed through the magnetic field of the electro magnet against a friction surface which is positioned at the magnet body. When the electromagnet is turned off, the disc shaped brake rotor is axially pressed by a spring against the planetary carrier, through which at least one locking element engages in a respective recess of the planetary carrier, wherein the planetary transmission is blocked in itself and rotates rigidly. When the electromagnet is turned on, the brake rotor is pulled against the reset force of the spring axially to the outside and against the traction surface of the magnet body, wherein the coupling between the smaller sun gear, and the planet carrier is eliminated and the smaller sun gear is decelerated accordingly based on the effective brake torque.
In accordance with its functional construction, a largely identical actuator device for the phase adjustment of a countershaft is published in the DE 10 2006 028 554 A1. Different from the previously mentioned actuator device, the phase shifter gearbox of this actuator device is designed as a simple planetary transmission with a sun gear, a planetary carrier which carries several, rotatably positioned planetary wheels and a ring gear, whereby the first input element is formed through the planetary carrier, the second input element through the sun gear, and the output element through the ring gear.
However, an additional type of actuator device for phase adjustment of a camshaft in accordance with DE 10 2008 043 673 A1 has an inverse control characteristic. The phase shifter gearbox is, like in the actuator device in accordance with DE 10 2006 028 554 A1, designed as a simple planetary transmission. However, the brake rotor which is rotationally fixed and axially shiftably positioned on a rigid shaft, which is connected with the sun gear, is hereby axially positioned outside of the electromagnet and clamped, by a spring, axially with reference to a freely rotatably positioned pressure disc. The pressure disc is axially positioned within the electrical magnet, adjacent the planetary carrier, and as cams to engage in recesses of the planetary carrier and for control lugs of the ring gear, which locks the planetary carrier with the ring gear in an emergency operating position, when the electromagnet is turned off. In addition, the brake rotor is pressed, when the electromagnet turned off, by a spring against an enclosure-fixed friction surface. When the electromagnet is turned on, the pressure disc is pulled axially away from the planetary carrier against the reset force of the spring and thus locking between the planetary carrier and the ring gear is eliminated. At the same time, the brake rotor is pulled away axially from the enclosure-fixed friction surface in accordance with the strength of the magnetic field against the reset force of the spring, and thus the effective brake torque is reduced.
Disadvantageously in these known actuator devices for a phase adjustment of the camshaft is the permanent energy consumption of the electromagnet during operation of the combustion piston engine and the respective actuator device. Also, in each case of the actuated devices a relatively strong magnetic field is required, against the reset force of the spring, to achieve a sufficient large brake torque for the adjustment and holding of the respective phase angle of the camshaft.